prolog:xref_source_identifier/2

prolog:xref_source_identifier(+Src, -Id) is semidet[multifile, swish(lib/include)]
prolog:xref_open_source(+File, -Stream) is det[multifile, swish(lib/include)]
prolog:xref_source_time(+File, -Modified) is det[multifile, swish(lib/include)]: Map swish://file to a file from the gitty store.
prolog:xref_source_identifier(+Object, -Ref)[multifile, library(pce_prolog_xref)]: The cross-referencer runs faster if the reference is an indexable term. Therefore we strip the XPCE @ from the object.